In recent years, in the field of radio communication, especially in mobile communication, a variety of information such as images and data in addition to voice is transmitted. The demand for higher-speed transmission is expected to further increase in the future, and, to perform high-speed transmission, a radio transmission technique that utilizes limited frequency resources more effectively and achieves high transmission efficiency is in demand.
OFDM (Orthogonal Frequency Division Multiplexing) is one of radio transmission techniques to meet these demands. OFDM, which is a multicarrier communication techniques for transmitting data in parallel using a large number of subcarriers, and is known to have features of providing high frequency efficiency and reducing inter-symbol interference under a multipath environment and be effective to improve transmission efficiency.
Studies are conducted that a radio communication base station apparatus (hereinafter simply “base station”) frequency-multiplexes data for a plurality of radio communication mobile station apparatuses (hereinafter simply “mobile stations”) on a plurality of subcarriers using this OFDM on the downlink.
Further, studies are underway to adopt ARQ (Automatic Repeat Request) for data transmitted from a plurality of mobile stations to the base station on uplink, and frequency-multiplex and code-multiplex a response signal showing an error detection result of uplink data on a plurality of subcarriers using OFDM. An ACK (Acknowledgment) signal is fed back if there is no error on uplink data and a NACK (Negative Acknowledgment) signal is fed back if there is an error, on uplink data as response signals to the mobile stations. Further, these response signals are transmitted on DPCCHs (Dedicated Physical Control Channels). Further, in DPCCHs, transmission power is controlled for each mobile station. That is, a plurality of DPCCHs for which the transmission power is controlled individually are frequency-multiplexed and code-multiplexed on a plurality of subcarriers. At this time, as shown in FIG. 1, DPCCHs (DPCCH 1 and DPCCH 2) for mobile stations near the center of a cell (MS 1 and MS 2) are controlled at low transmission power, and DPCCHs (DPCCH 3 and DPCCH 4) for mobile stations near cell boundaries (MS 3 and MS 4) are controlled at high transmission power, and the DPCCHs are frequency-multiplexed and code-multiplexed on a plurality of subcarriers (f1 to f8).    Non-patent Document 1: 3GPP RAN WG1 Meeting document, R1-061900, “Downlink Acknowledgment and Group Transmit Indicator Channels”, Motorola